Japanese Patent Laid-Open Publication No. 05-21865 discloses a method of forming rare earth thin film magnet on a substrate such as a glass substrate, quartz substrate, and silicon wafer by a spattering method. In the Publication, a method of forming a metallic layer between the substrate or the like and the rare earth thin film magnet is disclosed. A spattering method is generally employed for forming rare earth thin film magnet.
Japanese Patent Laid-Open Publication No. 06-151226 discloses a rare earth thin film magnet in that a metallic layer of about 1 to 40 nm in film thickness and an R2Fe14B (R is rare earth element including Y) alloy layer of less than 5 μm in film thickness having anisotropy in the direction of film thickness are alternately laminated to form rare earth thin film magnet by a spattering method. Japanese Patent Laid-Open Publication No. 08-83713 discloses optimum manufacturing conditions in a spattering method for rare earth thin film magnet having Nd2Fe14B as main phase: that is, substrate temperature of 530 to 570° C., film-formation speed of 0.1 to 4 μm/hr, and gas pressure of 0.05 to 4 Pa.
Further, Japanese Patent Laid-Open Patent Publication No. 09-162034 discloses a film magnet having multi-layer alloy film in that a hard magnetic layer comprising so-called rare earth magnet such as Nd2Fe14B, SmCo5, Sm (Co, Fe, Cu, Zr)7, SmFe11Ti, Sm2Fe17N2, and a soft magnetic layer such as Fe, Fe—Ni, Fe—Co, Fe—Si, Fe—N, Fe—B are alternately laminated. The laminated multi-layer alloy film structure comprises the hard magnetic layer having a thickness of 2 to 4 nm per layer manufactured by a spattering at a substrate temperature of 450 to 800° C. and having anisotropy in the direction of thickness; and the soft magnetic layer having a thickness of 6 to 12 nm per layer manufactured by a spattering at a substrate temperature of 150 to 650° C. and having anisotropy in the direction of thickness.
Also, Japanese Patent Laid-Open Publications No. 09-237714 and No. 11-214219 disclose a multi-layer rare earth thin film magnet of 5 to 500 nm thick, in that a soft magnetic layer and a hard magnetic layer are formed adjacent to each other in a in-plane direction of a film, and formed, for example, by a spattering method at substrate temperature of 300 to 800° C. and are strictly controlled in thickness at nm level.
However, in the manufacturing of rare earth thin film magnet by a spattering method, it is necessary to heat the substrate up to 450° C. at least, and moreover, the film-formation speed is as low as 0.1 to 4 μm/hr. Particularly, in the case of a rare earth thin film magnet having Nd2Fe14B as main phase, the film thickness is limited to less than 5 μm in order to suppress the lowering of coercivity due to oxidation. Also, in the case of a multi-layer rare earth thin film magnet of 0.01-300 μm thick with the thickness of soft magnetic layer and hard magnetic layer strictly controlled at an nm level, the method of manufacturing the magnet is more complicated and less economical.
In Japanese Patent Open-Laid Publication No. 11-288812 R—Fe—B based rare earth thin film magnet (hereafter R stands for rare earth element) is disclosed which is heat-treated after film-formation by a spattering method without heating the substrate. However, this method also involves problems such that the film-formation speed is less than 4 μm/hr and that the film thickness of the magnet is limited to less than teen μm.
On the other hand, there is a strong demand for miniaturization of electromagnetic motors and actuators. The points for miniaturization of motors and actuators are to reduce the number of components and to simplify the assembly. In this respect, the mover of a miniaturized motor or actuator is generally configured by using rare earth sintered magnet manufactured by a powder metallurgical process or rare earth bond magnet manufactured by forming spun-melt magnetic powder into a specific shape with use of resin.
Also, there are two types of motors, from the positional relations of magnet and armature coil. One type is an axial air gap type wherein the magnet and armature coil have gaps in the axial direction and another type is a radial air gap type wherein the magnet and armature coil have gaps in the radial direction. However, in a case of a millimeter-sized motor or actuator (axial air gap type) of 5 mm in diameter and 1 mm in height as shown in FIG. 1, which is an object of the present invention, it is also necessary to manufacture the rare earth magnet of the mover by 300 μm or less in thickness.
In FIG. 1, reference numeral 1 shows rare earth magnet; 2 a rotary shaft; 3 a bearing; and 4 an armature coil.
The crystal grain size of R-TM(transition metal)-B based rare earth sintered magnet is generally as large as 6 to 9 μm, and since there exists an R rich layer in the grain boundary, the magnetic performance of the surface layer is deteriorated during grinding operation, reaching as deep as about several tens μm from the surface. Also, since the material is brittle and hard to process, the processing limit taking into account the yield is estimated to be about 300 to 500 μm, and it is difficult to apply to such a millimeter-sized motor as shown in FIG. 1.
On the other hand, the crystal grain size of R-TM-B based rare earth bond magnet is as small as 20 to 100 nm, and when the grain size is less than 50 μm, the coercivity tends to become more dependent on the grain size. As a result, if the magnet is thinned, it will be unable to avoid the lowering of the magnetic performance due to worsening of the powder magnetic characteristic and lowering of the magnet density. Thus, the processing limit taking into account of a maintenance of magnetic performance and a production yield is estimated to be about 300 to 500 μm.
As described above, in the case of a millimeter-sized motor or actuator, it is not possible to make use of an original magnetic performance of rare earth magnet by employing the rare earth sintered magnet or the bond magnet manufactured by bonding spun-melt rare earth magnetic powder with resin.
When a motor or actuator is miniaturized, the electromagnetic force is proportional to the third power of the dimension according to the scaling rule. Therefore, for example, when the mover (magnet) becomes reduced to 1/10in size, the electromagnetic force is decreased to 1/1000. Accordingly, in case rare earth thin film magnet of less than 5 μm in film thickness is used as a mover, it is unable to obtain an electromagnetic force corresponding to the load in actual use.